In many currently produced automotive vehicles, the brake systems are both manually applied, with power assist, and self applied during anti-lock operation and in some vehicles during traction control of the driving wheels. During manual brake application, the operator depresses the brake pedal to determine the amount of braking pressure that will develop in the system at the braking wheels. During self-apply braking, the system pressure is established by a system regulator valve.
The regulator valve sets the maximum system pressure at a fixed value regardless of the system requirements. The excess fluid flow is exhausted through the regulator valve resulting in noise and vibration from the hydraulic system which is discernable by the operator. While this occurrence is not detrimental to the braking system or the vehicle, it can be disconcerting to the operator when it occurs unexpectedly.